Vortex diodes are among the useful fluidic devices, which do not have any moving components. The basic design of a vortex diode consists of a disc-shaped chamber with cylindrical axial and tangential ports, but the devices have been modified over the years by many researchers and designers to improve their function as well as to use them for purposes other than as valves.
Effluents from various industries such as chemical, paper and pulp, tannery and such like have the issue of high Chemical Oxygen Demand (COD), while the limit set by Pollution Control Board usually does not exceed 250 mg/l for industrial wastewaters. Chemical Oxygen Demand commonly represents the amount of organic compounds/pollutants in water and is an important parameter in water analysis, especially for wastewater treatment for the protection of environment. Several chemical methods are known in the art for treating effluent to control COD based on ozone, hydrogen peroxide, steam, oxygen, charge neutralizing species/coagulants and others. A few physical methods also exist for the treatment of waste waters viz. filtration, electrooxidation, electro-coagulation, froth floatation, adsorption, etc. There are certain organic pollutants, especially in dyes/pigments/colorants/textile wastewaters, which are considered refractory compounds difficult to remove/degrade by using conventional methods of chemical/biological treatment. For such pollutants, newer techniques have to be explored where extreme conditions can break down pollutants and organic molecules.
There are number of industries such as textile and dyeing industries that use many kinds of dyes, both reactive and non-reactive, and discharge large amounts of highly coloured wastewater. This effluent must be treated prior to discharge in order to comply with the environmental protection laws for the receiving waters. The biological treatment processes that are frequently used to treat textile effluents are generally efficient for meeting limits of Biological Oxygen Demand (BOD) and Total Suspended Solids (TSS) removal but are largely ineffective for removing colour from the wastewaters. Consequently effluents many times contain appreciable amounts of colour. This water though can pass as suitable for discharge fails the criteria for recycle and reuse. Other methods of physico-chemical treatment operations, including adsorption, oxidation, chemical precipitation etc. are also reported in literature with little success.
Most of the existing wastewater treatment methodologies differ significantly from each other not just in their principles, but in the form of application, process economics with huge differences in land, equipment and material requirements. Further, since effluent treatment is more complicated due to varied types of pollutants including organic and inorganic pollutants, new strategy is required involving novel materials, methods and process integration options/technology for wastewater treatment.
Cavitation technology in recent years is found to be substantially beneficial in waste water treatment. Cavitation is a phenomenon of formation, growth and collapse of micro bubbles within a liquid. Cavitation occurs due to increase in kinetic energy of the fluid at the expense of local pressure when the fluid passes through constriction. Hydrodynamic cavitation known in the art utilizes constriction such as orifice/venturi in the path of flow of fluid. Moreover, cavitation is realized due to linear velocity of liquid in conventional devices. Vortex diode disclosed in this invention on the other hand uses rotational flow to generate cavitation. The nature of cavities (number density of generated cavities and intensity of collapse of generated cavities) in such rotational flows realized in vortex diode is significantly different than the other hydrodynamic cavitation devices known in the art as orifice/ventury which are based on constriction of the flow.
U.S. Pat. No. 4,112,977 discloses a vortex diode wherein the tangential ports can be formed as push-fit into the main body of the diode. It is recommended to have as many tangential ports as possible to improve flow symmetry and reduce pressure losses.
U.S. Pat. No. 6,358,415 titled “Vortex sewage disposal apparatus” relates to a vortex sewage disposal apparatus for the disposal of construction sewage.
The vortex diode as an apparatus which uses cavitation and collapse of cavities generated due to rotational flows has been hitherto unexplored for the treatment of effluents. Particularly, the effluents generated from highly polluting industries such as dye, pigments and other colour effluent generating industries that also generate effluent with high COD, ammoniacal nitrogen or color have not been subjected to cavitation treatment by a vortex diode.